The present invention relates to modified thermoplastic poly(C.sub.2-6 alkylene terephthalate) molding compositions which in preferred instances provide molded articles possessing improved impact resistance, lower specific gravity improved resistance to distortion under load, and improved surface appearance. More particularly, the invention relates to compositions of (a) a (C.sub.2-6 alkylene terephthalate) resin, and a major proportion of (b) an aromatic polycarbonate resin combined with (c) a polyolefin or an olefin copolymer.
The invention includes articles molded from the composition.
High molecular weight linear polyesters of C.sub.2-4 glycols with terephthalic acid (and isophthalic acid and other similar dibasic acids) have been available for many years. Certain of these are described in Whinfield et al. U.S. Pat. No. 2,465,319, and in Pengilly, U.S. Pat. No. 3,047,539, incorporated herein by reference.
With the development of molecular weight control, the use of nucleating agents and two-step molding cycles polyethylene terephthalate and, in general, the poly(C.sub.2-6 alkylene terephthalate) resins have become important constituents of injection moldable compositions. Poly(1,4-butylene terephthalate), because of its very rapid crystallization from the melt, is uniquely useful as a component of such compositions. Workpieces molded from such polyester resins, alone or combined with reinforcements, in comparison with other thermoplastics possess a high degree of surface hardness, abrasion resistance and gloss, and a low degree of surface friction.
Stable polyblends of poly(1,4-butylene terephthalate) and polyethylene terephthalate can be molded into useful unreinforced and reinforced articles. See Fox and Wambach U.S. Pat. No.3,953,394, incorporated herein by reference.
Block copolyesters containing units derived from poly(1,4-butylene terephthalate) and from an aromatic aliphatic or aliphatic polyester are also known. See copending application U.S. Ser. No. 752,325, filed Dec. 20, 1976, incorporated herein by reference. Such block copolyesters are useful alone as molding resins and also in intimate combination with poly(1,4-butylene terephthalate) and/or polyethylene terephthalate.
Polycarbonates are known to be admixable with various polyesters, including poly(alkylene terephthalates). Such blends are often more cost effective than the polycarbonate alone. Compositions of polycarbonate resins and polyester are disclosed, for instance, in U.S. Pat. No. 3,864,428 (Nakamura, et al.).
Bussink et al. in U.S. Pat. No. 4,267,096 disclose compositions comprising a selectively hydrogenated elastomeric block copolymer, a polycarbonate and an amorphous polyester. These compositions are described as having improved melt flow and resistance to brittle failure and environmental stress cracking.
Dieck et al. in U.S. Pat. No. 4,220,735 disclose thermoplastic compositions of poly(1,4-butylene terephthalate) resin in combination with poly(ethylene terephthalate) and/or a polyester copolymer and a modifier comprising both a selectively hydrogenated monoalkenyl arene-diene block copolymer and an aromatic polycarbonate.
It has been proposed to increase the impact strengths of such polyesters by adding modifiers. For example, Brinkmann et al. in U.S. Pat. No. 3,591,659 disclose that a useful family of modifiers comprises polyalkyl acrylates, methacrylates and/or ethacrylates. Baron et al. in U.S. Pat. No. 4,044,073 disclose that a useful impact modifier for such polyesters is an aromatic polycarbonate. Schlichting et al. in U.S. Pat. No. 4,022,748 disclose that a rubber-elastic graft co-polymer having a glass temperature below -20.degree. C. is a useful modifier. Lane, U.S. Pat. No. 4,034,013 and Farnham et al., U.S. Pat. No. 4,096,202 disclose that useful impact modifiers comprise multiple-stage polymers having a rubbery first stage and a hard final stage, preferably including units derived from alkyl acrylates, especially the butyl acrylates. Baron et al. in U.S. Pat. No. 4,034,016 disclose an impact modifier combination comprising a blend of polyurethane and an aromatic polcarbonate. Co-pending application Ser. No. 870,679 filed Jan. 19, 1978, now U.S. Pat. No. 4,203,887, discloses an impact modifier combination comprising a segmented block copolyester and an aromatic polycarbonate. and Cohen et al. co-pending application Ser. No. 957,801, now U.S. Pat. No. 4,257,937, discloses combinations of polyarylate resins and aromatic polycarbonate resins for the purpose. Reinforced, filled and/or flame retardant modifications of such polyesters are also well-known in the art.
It has now been discovered that molding compositions comprising a minor amount of poly(C.sub.2-6 alkylene terephthalate) resin, including copolyesters thereof, provide moldings of improved impact resistance, flexural and tensile strength and resistance to distortion at elevated temperature under load, as well as lower specific gravity, improved compatibility without delamination and improved surface appearance, when the compositions include an intimate admixture of a polycarbonate resin and a polyolefinic or olefin copolymer resin.